By the methods of single crystal x-ray structure determination, we propose to obtain structural details of the way in which barbiturate molecules associate with each other and with molecular species which are representative of biological systems, such as water, peptides and lipids. Barbiturate crystal structures exhibit an unusually wide variety of intermolecular interactions, including ionic bonding, hydrogen bonding, van der Waals interactions between flat pyrimidine rings or between non-polar hydrocarbon groups, dipole-dipole interactions between carbonyl groups. We aim to establish principles which govern barbiturate intermolecular behavior in the crystalline state, so that by judicious extrapolation, there will be a useful guide for proposing models for molecular behavior in vivo, where direct observations of structural aspects of barbiturate molecular interactions are impossible at this time.